The invention relates to polymer coated optical fibers and, more particularly, to reducing interfacial shearing stress in such fibers.
Polymer coatings are widely used on silica optical fibers to improve reliability of the silica material, which is both brittle and moisture-sensitive. Conventional coatings are made of a single polymer material. Although they may enhance the reliability of the silica, they may delaminate therefrom, reducing their effectiveness and possibly damaging the system in which they are used.
Delamination occurs primarily because of dissimilar materials in the coated fiber. Dissimilar materials may cause thermally induced stresses in the polymer-coated optical fiber when the structure is manufactured at an elevated temperature and is subsequently cooled down to a lower temperature. These stresses force the coating apart from the fiber. Coatings having properties, such as coefficients of thermal expansion, that would reduce the thermal stresses, may not provide adequate protection of the silica material. Accordingly, there is a need for an optical fiber coating less susceptible to delamination than conventional coatings, and that adequately protects the optical fiber.
Thermally induced stresses in coated optical fibers may be reduced by coating portions of the fiber with materials of different Young""s moduli, thereby decreasing occurrences of delamination as compared to a fiber with a single material coating.
Embodiments of the invention provide an optical fiber having a multi-material coating and a fabrication method therefor. The coating includes at least two portions adjacent in a longitudinal direction. Adjacent portions are made of different materials having different Young""s moduli. In an illustrative embodiment, the coating has two end portions and a mid-portion therebetween. The mid-portion comprises a material different from that of either end portion. Each end portion material has a lower Young""s modulus than that of the mid-portion.
The interfacial shearing stress for the multi-material coated fiber can be substantially lower than the interfacial shearing stress for a similar fiber coated with only one of the materials found in the multi-material coating. For example, in an embodiment of a coating having a mid-portion and two end portions, the interfacial shearing stress of the multi-material coated fiber is less than that of a substantially like fiber coated with only the mid-portion material to substantially the same thickness as the multi-material.
Further disclosed is a telecommunications system and fabrication method, wherein the system comprises multi-material coated fibers having reduced interfacial shearing stress.